Aminotriazine-aldehyde binding agent



Patented May 4, 1943 I AMINOTRIAZINIA'I- ALDEHYDE nmpmc GENT GustavWidmer, Basel, and Willi .Fisch, Muttenz, near Basel, Switzerland,assignors, by mesne assignments, to Ciba Products Corporation,

Dover, Del., a corporation of Delaware No Drawing. Application July 27,1937, Serial No. 156,034. In Switzerland August 1, 1936 3 Claims.

The present invention is concerned with the use of condensation productsof aminotriazines and aldehydes as binding agents. It comprises theimproved process of using said binding agents in the different fields ofapplication as well asthe improved binding agents themselves and thematerials resulting from the treatment with said binding agents.

The use of artificial resins capable of being hardened, for examplethose from phenol and formaldehyde or urea and formaldehyde as bindingagents for various purposes is known. The resins have the advantage thatthey can easily be applied as an adhesive in an unhardened condition inthe form of a solution, a powder or suspension and then hardened toconvert them into a highly insoluble form. However, owing to variousdisadvantages their application for many of the industries in whichbinding agents are required is limited.

The phenol resins are not useful in aqueous solutions and in generalrequire a high temperature, for example IUD-170 C., for the hardeningoperaticn. In the form of a cold-hardened mixture they require a largeproportion of a hardening agent of an acid nature which is permissibleonly in a limited number of applications, for instance in acid cements.For many uses the instability of the phenol resins to light is aninsurmountable disadvantage. Also urea resins which have the advantageof-solubility in aqueous media require nearly as high a temperature forthe hardening operation. In this case, indeed, cold hardening products.for example, cold glue, are known, but

in comparison with the phenol resin glues they have a limited resistanceto hot water. In particular the urea resins cannot be satisfactorilyhardened with a weak acid but always require a strong acid or strongacid salt, either of which is liable to damage materials glued togetherwith the adhesive; cellulosic materials are an example.

The present invention relates to a process of gluingwhich minimizes oravoids the foregoing disadvantages by the use as an adhesive of thecondensation products capable of being hardened which can be producedfrom formaldehyde and an aminotriazine, for example an aminotriazinecapable of being produced by the process described in the copendingapplication Ser. No. 68,355, filed March 11, 1936. These products haveproved to be surprisingly reactive so that the adhesives, cements, gluesor the like made therefrom can be hardened or made insoluble in watertrue that in the aforesaid specification it has already been said thatthe condensation products from formaldehyde and amino-triazines areuseful as binding agents, for example, for ply-wood, however there arementioned there hardening temperatures of C. and corresponding hardeningtimes of 30 minutes.

It has now been found that these new condensation products can be usedunder substantially milder conditions of temperature, particu-- larlyalready at temperatures well below 100 C. or even at room temperature asa glue which is stable not only to cold water but also to boiling water.The new adhesives therefore are suitable for a large number ofapplications for which the hitherto used artificial resins capable ofbeing hardened cannot be used on account of their defects.

For gluing wood, particularly ply-wood and veneers, urea formaldehydeand phenol formaldehyde resins have been used. Urea resins, however, donot provide a glue fast to boiling water, that is to say a glue whichcan be subjected to the action of boiling water for 24 hours] or longerwithout dissolution of the film of glue. On the other hand water-proofglues may be produced from phenol resins. The gluing may b done withvarious forms of the phenol resin, either by film gluing, whereby thereis used as carrier a thin paper, or the resin may be used inan aqueoussuspension or an, alcoholic solution. Whatever the form it is not sosatisfactory as the application of an aqueous solution in the industriesrequiring glue since the hardening temperature of, for example, C.necessary for the phenol resins is a great draw-back not only becausespecial hot presses are needed but also because the wood suffers.

The adhesives used according to the present invention yield a hot waterstable glue, and especially have the formaldehyde condensation productsof the 2.4.6-triamino-1.3.5-triazine proved suitable for the purpose.

The speed of hardening of these new glues may be varied greatly by theuse of accelerators of used the glue can be applied at a moderatetemperature, for example 70-90 C., and the gluing will be remarkablyfast to boiling water. Indeed,

objects which are glued with this material may be in contact withboiling water for days before the parts fall asunder by destruction ofthe film of lue.

1 11 the presence of large proportions of the accelerator the hardeningis so rapid as to occur even at room temperature, for example onstanding overnight. The quality of this gluing with respect to boilingwater is of the same order as that of the hot gluing, which issurprisingly new for a cold glue.

The new adhesives may be used pure or in admixture with the usualfilling and extending agents of organic or inorganic nature. Kaolin,gypsum, asbestos, barium sulfate or the like are examples of inorganicfilling agents and ivory nut fiour, soya bean flour, rye flour, starchand so on are examples of organic filling agents. The addition ofwater-repelling substances such as paraffin or aluminium salts can berecommended.

The new adhesives are advantageously produced in the form of drypreparations which may contain the binding agent, the filling agent and,if necessary, the accelerator-and the like in suitable admixture so thatthe user can convert the preparation into a liquid glue ready for use bysimply mixing it with water. These dry preparations are quite suitablefor storage, whereas liquid condensation products have generally alimited capacity for storage. Such dry preparations may, of course, bebrought into the form of the known glu films.

The use of the new glues is not limited to a production of ply-wood andveneers. In the form of cold hardening glue the products open upv fungiunder conditions which are rapidly fatal.

to casein glue or animal glue. They are therefore much better stable toweather and may be used for joining wood which is exposed to weathering,for instance ply-wood huts, ply-wood slabs for cement mouldings,ply-wood for building constructions, autocar bodies, aeroplaneconstruction, boat-building and so on.

'I'henew adhesives, however, are applicable for many other purposes, forexample, for fixing wall-papers, that is to say, for papering andotherwise decorating dwelling rooms or other surfaces. They are suitablefor art papers or velvet papers in box making. They maybe also used forsaturating fabric with the solution of the binding agent and thenapplying the fabric in wet condition for instance for lining motorcartrunks. In like manner the binding agent may serve for fixing sail clothin the making of fiber trunks, for fixing the insertions and linings ofordinary trunks and the like. In all these cases by suitably compoundingthe glue with the use of the new binding agent there is produced a unionof the glued material with the support by drying at ordinarytemperature, and the union is fast to boilin water.

Textile materials which have been impregnated with the new adhesive mayalso be used for surgical purposes, for example a gauze bandage may beimpregnated therewith and wound in wet condition around the part of thebody which is to be shaped or protected; after a short time at a moderattemperature or at the room temperature the layers thus formed harden andnot only possess considerable strength but are completely insensitive towarm water or bath water.

This possibility of shaping is also important in orthopaedy. Plaster ofParis or starch bandages which have generally been used for this purposehave the disadvantage that they are heavy or sensitive to water.

A further application for the new adhesive is as a cement or paste. Forcements for making brushes it is suitable on account of its lowhardening temperature, simple mode of application in aqueous solution,good water-proof character and lack of odor. In many usual cements formaking brushes the high temperature of hardening and the long durationof hardening causes damage to the brush hairs. Also spreading pastes maybe made with the new binding agent, the ordinary filling agent such askaolinfbeing added; such a paste will dry overnight at the ordinarytemperature to a hard water-proof surface which will withstand boilingwater if necessary and on which a. top coating such as varnish may beeasily and faultlessly applied. If

fine wood fiour is used there may be produced in like manner a hardeningwood mass which can be used for obliterating wood knots, cracks,fissures and cavities in wood or the like, as is required in thewood-working industry or in the household.

The new adhesive is also suitable for making artificial cork, theproduct being produced in a form fast to boiling water and tasteless andodorless at a very moderate temperature, indeed even at roomtemperature.

A further application is for the production of waterproof sizings in thepaper industry for which the absolute fastness to light, the freedomfrom color and smell of the binding agent particularly fit it. Here alsothere is the advantage of rapid hardening which may occur in theordinary course of manufacture, for instance by the gentle heat ofcalendering. In its water-soluble form the new binding product serves,in combination with the usual pore fillers, pigments and the like, as aspreading paste which may be applied to the paper by means of a rolleror doctor blade. dried and hardened by the dry moderately heatedcalender or in the cold. Lustrous and matt surfaces of any-color,water-repelling or absorbent and of a high degree of stability to watermay be produced in this manner. In its water-insoluble form the newbinding agent may be added to the hollander for sizing the paper pulp.For satisfactory working in an aqueous medium the binding agent may beused in the form of an acid solution from which the insoluble product isprecipitated in the fiber in the hollander by the addition of a base oralkali. For making waterproof fibrous plates for insulating andconstructional purposes and also water-proof artificial wood platescheap fibrous material such as woodpulp, straw, corn stalks or the likemay be beaten in the hoilander and the new binding agent may be used inthe form of an acid solution of the hydrophobe resin and precipitated onthe fiber in presence or absence of another filling material and bindingagent by means of a neutralizing agent. In this manner mechanicallystrong products which are odorless and do not mildew and are of verygood stability to water may be obtained. 4

The new adhesive is also useful in the industry of water paints(size-colors or distempers). At the present time such water paints aremade on a basis of animal size when used for internal painting and ona-basis of casein for external painting, but they have a limitedstability to weather and water. With the new adhesive water paints maybe made which are of considerably enhanced stability to water ascompared with size colors or casein colors so that the water paint artis extended by their use. In this case it is obvious that there can onlycome into question a product which hardens at ordinary temperature andis insoluble. Such water paints when made with a suitable thickening arealso applicable as printing colors on paper or textile fabric. Colorsfor the textile industry may be made in this manner with the use ofpigments of organic or inorganic nature and they prove quite stable tosoaping at the boil. The use of albumen or casein for producing likeeffects is known and the albumen prints are stable to water. Neither ofthese binding agents, however, is stable to soaping at the boil. Printedpapers made with the aid of the water paints are useful for makingdecorated laminated material in the artificial resin moulding industry;for they do not exhibit like the usual paper printed with oil varnishwater-repellent properties, for instance as compared with aqueousartificial resin solutions, but on the other hand they can. beimpregnated therewith without difficulty.

Finally the new binding agents serve as waterproof fixing for dustingagents which are used to combat animal and vegetable pests. For thispurpose a dusting agent to be used as a fungicide or insecticide, forexample lead arsenate, arsenious acid, copper compounds, mercurycompounds, sulfur or sulfur compoundafiuorine compounds, vegetableextracts such as pyrethrum, nicotine or the like may advantageously besus-.

' pended or dissolved in an aqueous solution of the new binding agentand sprayed upon the surface to be protected, namely plant, animal orobject,

there being added to the solution so much accelerator of the hardeningthat the product 'becomes insoluble in cold water within a few hours,Since in this manner the protective substance remains effective for along time, for instance throughout the whole of the vegetation period ona plant because it is not washed away by the rain, the use of the newfixing agents constitutes a great advantage. If desired the surfaceactivity of the solution may be increased by the addition of a wettingagent or the like or by the addition of an agent which improves itsadhesiveness, for instance an oil or a resin.

'It will be understood that the foregoing enumeration of some of themore important applications of the new binding agents is not exhausted.On the contrary there are numerous other industries in which the agentsare useful.

The application of the new adhesives is not limited to the use ofpreformed condensation products of the aminotriazines. On the contrarymixtures of the components may be used. The components may be appliedsuccessively or in the form of separate solutions. Methylol compounds ofthe respective aminotriazine may also be used. The expressioncondensation products soluble in aqueous media is intended to includethose which are insoluble as free resin bases but, can be obtained inaqueous solution in presence of acids as resin salts.

The condensation products used according to this invention as well astheir manufacture are described at length in the copending appllcatiomSer. No. 68,355. Among such condensation products there may for instancebe mentioned the formaldehyde condensation products of the followingaminotriazines: 2.4.6 triamino-1.3.5-triazine (melamine) or deaminatedproducts thereof, for instance melam; further 2-chloro-4.6-di.-amino-1.3.5-triazine, 2 hydroxy 4.6 diamino- 1.3.5-triazine (ammeline)and so on.

While the 2.4.6-triamino-1.3.-5-triazine-formaldehyde condensationproducts have proved particularly useful for the purpose of the presentinvention, the use of all the other condensation products forming thesubject of the said copendmg application is intended to be included inthe present application.

The following examples illustrate the invention, the parts being byweight; The relationship between parts by weight and parts by volume isthat which exists between the kilogram and the itre.

' EXAMPLE 1 A manufacture of triazine pure resin by volume of neutralformaldehyde of 30 per cent. strength by volume and the suspension keptin the water bath, the internal temperature of which is 80 C. Thetriazine dissolves in a few minutes. The condensation is continued untila sample withdrawn, cooled and diluted with 3 parts by volume of watershows a milky turbidity which is normally the case in about half anhour. The mixture is now quickly cooled and evaporated in a vacuum atlow temperature to a thick syrup and the latter is immediately dried ina vacuum chestin the form of thin layers and then ground. Thecondensation solution may alternatively be dried by scattering or in aroller dryer. The dried powder thus obtained can be stored well and iseasily soluble in water. It constitutes a binding agent for thefollowing examples of gluing: (a) 100 parts of the triazine pure resinare mixed with 100 parts of barium sulfate and 1 part of oxalic acid andstirred with 60 parts by volume of water to form a glue which can bespread. This glue is applied to a wood veneer, the glue coating beingabout 150-200 veneer is layered with crossing of the layers in the usualmanner and then hardened in the hot press for 30 minutes at 80 C. undera pressure of at least 4 kilos per square cm. The veneer plate thusobtained was tested in boiling water which it withstood for 116 hoursbefore the several veneers began to separate from each other.

'(b) 100 parts of the triazine pure resin are mixed with 5'parts ofammonium sulfate and the mixture is stirred with 45 parts by volume ofwater to form a glue solution capable of being spread. This solution isused for making a plywood sheet which is kept for 16 hours at roomtemperature in the press or clamped under pressure. A test piece of thissheet is subjected to boiling water after 24 After 150 hours of boilingthe gluing is still completely intact.

(c) 100 parts of the triazine pure resin are mixed with 100 parts ofgypsum powder and the mixture is stirred with 90 parts by volume ofwater containing 1 part by volume of formic acid.

As in the preceding example a ply-wood sheet is constructed with thisglue and allowed to harden overnight in a cold press. After storage for24 hours it is tested in boiling water. After 150 hours boiling thegluing is still completely intac (d) parts of the triazine pure resinare 126 parts of 2.4.6-triamino-l.3.5-triazine (melamine) aresuspendedwhile stirring in 300 parts grams per square metre calculated on the dryresin, and the wood hours storage in the air.

of the sheet after 24 hours storage in the air is subjected toboilingwater. Separation of the layers begins after about 24 hours.

(e) 100 parts of the triazine pure resin are mixed with 50 parts of ryeflour and 50 parts of pot to starch as well as 4 parts of potassiumpersulfate. For making the liquid glue there are used 8 parts by volumeof an aqueous paraiiln emulsion of 5 per cent. strength containing anemulsifier, for instance glue, and 110 parts by volume of water. Theliquid is used as described above for making a ply-wood sheet which iskept overnight under pressure at room temperature for hardening. A testpiece of the sheet after storage for 24 hours in the air is tested withboiling water; only after 44 hours does the separation of the layersbegin.

EXAMPLE 2 16 parts of the condensation product made as described inExample 1, paragraph 1, are dissolved while stirring in 8 parts byvolume of a solution of 10 percent. strength of ammonium sulfate andinto the viscous clear resin solution thus obtained there are graduallyintroduced while mixing well 30 parts of kaolin and 1 part of acommercial paraflin emulsion of 20 per cent. strength. By finallykneading there is produced a cement-like mass which can be applied likea normal spatula mass for covering unevennesses, fissures or the like ona support of any kind. The mass becomes stone-hard overnight and byexposure to air and forms a good grounding for the application of a topcoating, for instance of lacquer.

The mass can also be used for modeling bodies which on standing in theair for a few days become resistant to boiling water. The mass can becolored by any pigment or soluble dyestufi. By substituting fine woodflour wholly or in part for the kaolin there is obtained a mass capableof being molded which after hardening has a color resembling that ofwood and having other wood is further lined in the following mannerExams: 4

A motor-car trunk which is lined with plywith cloth which will notmildew in damp weather or by spilt liquids.

50 parts of the resin described in Example 1, paragraph 1, are dissolvedin 50 parts of ammonium sulfate solution of 5 per cent. strength to forma solution of low viscosity. Meanwhile the desired cloth is cut to makethe lining pieces.

, These separate pieces are impregnated with the properties resemblingWood which makes it suitable for filling knot-holes, fissures, etc., inthe time, about 2 hours, because they rapidly become unusable by gradualself-hardening.

EXAMPLE 3 Paint brush hairs are tied together in bundles in such amanner that the final 2 cm. of the bundle are freely exposed. The bundleis then dipped 1 cm. deep into a solution of the resin described inExample 1, paragraph 1, the solution containing 67 per cent. of resinand 33 per cent. of an ammonium sulfate solution of 10 per cent.strength. In the course of about a quarter of an hour the clear resinsolution soaks into the bundle of hairs and the latter is then freedfrom excess of resin solution by wiping and left to dry and harden for 1hour at 80 C. or for 8 hours at 35-40 C. or for some days at roomtemperature. In each case the hardening has so far proceeded that thebrush may be kept in boiling water for 1 hour without any change.

resin solution, squeezed out by hand and laid upon the ply-wood lining,which has been coated with the same solution, in wet condition.straightened andwell pressed down. After each or the walls of the woodenlining have been covered the box is left in a drying room for two days.The cloth is now indissolubly united with the wood and the gluing cannotbe destroyed either by mildew or wet. In like manner boxes can be linedwith velvet or the like. So also in this manner' wallpapers ordecorative material may be fixed to the walls of dwelling rooms, ifdesired with the addition of boiled starch as a stretching agent. Incase of supports which still contain free lime there should first beapplied a plas ter of Paris coating or the lime should be neutralized bya brushing of an ammonium sulfate solution of 10 per cent. strength orneutralized with'sulfuric acid whereby the acceleration of the hardeningof the binding agent may occur correctly.

EXAMPLE 5 10 parts of kaolin, 10 parts of a 30 per cent. strengthlithopone poor in zinc oxide and 5 parts of the dry resin described inExample 1, paragraph 1, are rubbed together with 12.5 parts by volume ofammonium chloride solution of 5 per cent, strength to form gradually auniform paste which is then diluted with 12 parts by volume of asolution of 5 per cent. strength of bone glue. This thin water paint isapplied to a wall which has previously been brushed over with anammonium sulfate solution of 10 per cent. strength or better with asulfuric acid solution. A white matt coating is thus obtained whichafter drying for two days at room temperature is fast to mopping and towater and does not strip from the support.

EXAMPLE 6 30 parts of a latex containing '70 per cent. of

rubber (commercial rubber milk) are diluted with solution. Into thismixture there is stirred a solution of 5 part of the dry resindescribed-in Example 1, paragraph 1, in 3 parts by volume of water andthe mixture after being thoroughly homogenized is poured on to 50 partsof cork dust. The whole is mixed until all cork particles have beenuniformly coated with a layer of liquid and the moist mixture is quicklymade up into a mold and compressed in clamps or a press. After standingovernight the artificial cork plate is removed from the mold and driedfor a further 24-48 hours in an airy room. There is obtained a goodelastic artificial cork which does not disintegrate even when boiled inwater for 1 hour.

EXAMPLE 7 20 parts of a lithopone of 30 percent. strength are rubbedtogether uniformly with 10 parts of a solution of 50 per cent. strengthof a triaminotriazine resin. This resin solution is made by condensing12.6 parts of pure triamino-tria'zine.

for instance melamine, with 30 parts of neutral formaldehyde solution of30 per cent. strength in a water bath at 80 C. and immediately cooling,as soon as, after about 20 minutes, a sample of the solution shows aturbidity on addition of 10 times its weight of water. The white mixtureis now well rubbed with 50 parts of a starch paste of 10 per cent.strength whereby a very flexible mixture is produced. This is now mixedbefore use with 0.25 part of ammonium sulfate in 1 part by volume ofwater; it is then spread on an unsized paper in a thin layer and dried.The reverse side of the paper can be similarly treated. After drying thepaper is passed through a heated satin calender whereby a white mattsizing is obtained which is fast to ink. If the calender is not heatedor is only feebly heated the property of fastness to ink is retainedonly after selfhardening for some days. The sizing may, however, becarried out in the Hollander method described in the next followingexample.

EXAMPLE 8 80 parts of wood-pulp calculated on dry sub stance are beatenin the Hollander with 4000 parts byvolume of water until the fibers areseparated. 320 parts of a starch paste of per cent. strength are thenintroduced followed by 8 parts of a hydrophobe triamino-triazine resinin the form of a sulfuric acid solution. This solution is made bycondensing 12.6 parts of pure triaminotriazine for instance melamine in30 parts of a neutral formaldehyde solution of 30 per cent. strength inthe water bath at 80 C. and then immediately cooling, as soon as afterabout 1 hour a drop of the condensation solution mixed. with 1 cc. ofwater shows thick flocks of precipitated resin. Of this solution, whichis of about 50 per cent. strength, 16 parts are used. Before introducingit into the Hollander this resin solution is precipitated by addition of100 parts by volumeof water and again cleared up by means of 30 parts byvolume of 2N-sulfuric acid. After the solution has been thoroughly mixedinto the Hollander with the wood-pulp 40 parts by volume of a commercialparaflin suspension of 5 per cent. strength and 8 parts by volume of analuminium sulfate solution of 25 per cent. strength are added. Theexcess of sulfuric acid is now neutralized by caustic soda solution of 8per cent. strength until Congo paper still shows brown, for whichpurpose 5-10 parts by volume arenecessary. The pulp is now formed in afilter press to a plate which is pressed to the desired thickness andthen dried at IO-80 C. and feebly super-pressed. The product is afibrous plate of wood-like properties which has good resistance towater.

EXAMPLE 9 60 parts of Cibanone Blue RS paste double (Schultz.Farbstofitabellen No. 1228) are rubbed with 600 parts of an aqueoussolution of 50 per cent. strength of the resin described in Example 1,paragraph 1, and 290 parts of tragacanth thickening which contains 60parts of dry tragacanth in 1000 parts by volume of water; before use 50parts by volume of concentrated formic acid are added.

The mixture is printed on a cotton fabric in the usual manner with anengraved brass or copper roller and the print ng is dried at 40-50 C.for half an hour in a drying chest. The printed fabric is now washedcold and then for 10 minutes soaped in a boiling soap solutioncontaining 3 parts of soap per 1000 parts by volume of water; hotrinsing, cold rinsing and drylngfollow. No trace of dyestufl' pigmentbleeds in the process. .The pigment is thus, by this treatment, fixedfast to soaping even at boiling temperatures.

EXAMPLE 10 5 parts of arsenious acid are well rubbed with 10 parts ofthe triazine resin solution made as described in Example 7 and 50 partsof a starch paste of 10 per cent. strength. Before use 0.25 part ofammonium sulfate and 5 parts by volume of formic acid are added and thewhole is diluted with 35 parts by volume of water. The suspension maynow be applied to the plants to be protected, where it forms afterdrying and standing for some sunny hours of the day a strongly adherentcoating which is not washed off by the rain.

EXAMPLE 1 1 A methylol compound of melamine is prepared as follows:

63 parts of melamine are dissolved, while stirring, on a boiling waterbath in 170 parts by volume of an aqueous solution of formaldehyde of 32per cent. strength by volume which has been neutralized with causticsoda solution, and immediately cooled in ice-water. After standingovernight the solution solidifies to a white mass, which is then brokenup into pieces of the size of a pea and dried in a current of air atabout 40 C. in about 3 hours. The product dissolves to a clear solutionin hot water.

(a) A printing paste is made up as follows: 25 parts of ivory black arewetted with 5 parts by volume of alcohol and 3 parts by volume of Turkeyred'oil. 30 parts by volume of a solution of 15 parts of the abovemethylol compound in 15 parts of water are then stirred into the mixturetogether with 30 parts of an aqueous gum tragacanth thickening of 6 percent. strength. Thereupon the mixture is made up with water to 100 partsby volume.

This paste is printed in the customary manner on a bleached cottonfabric, dried and then steamed for 5 minutes in a Mather-Flattapparatus. The material is then soaped in a solution containir. 3 gramsof soap per litre for 10 minutes at C., rinsed and dried. Deepblack'efterial there are obtained matt effects on a lustrous groundwhich are fast to soaping.

(c) If a mixture of ivory black and titanium white is used there areobtained in an analogous manner when using a bleached cotton fabric greyeffects on a white ground.

EXAMPLE 12 50 parts of fine corundum powder having a grain of mm. orfiner, are kneaded with 7.5 parts of the resin powder described inExample 1, paragraph 1, and 3 parts of water, which contains 10 grams ofammonium sulfate per 80 cc.

of water, and then stamped into round form. The latter is then subjectedin a press for 3 minutes at room temperature to a pressure of 180 kilosper square cm., the moulded article is then removed and hardened for 16hours at 80 C. A grinding disc of good strength is thus obtained.

EXAMPLE 13 The resin solution from 2.4.6-triamino-1.3.5- triazine andformaldehyde prepared as described in Example 1 is evaporated until asyrup is obtained, of which the viscosity corresponds approximately tothat of chemically pure glycerine. It is then used in a normalimpregnating machine, such as is used for example for impreg nating thinpaper with phenol-formaldehyde resin, for impregnating an unsized kraftpaper having a weight of about 20 grams per square metre and the treatedpaper is dried in known manner at 60-80 C. There is thus obtained a gluefilm having a weight of about 80-100 grams per square metre, which isnot more deeply colored than the untreated paper, is not hygroscopic andis odorless.

layers of undried birch veneer having a moisture content of about 14percent. are laid one upon the other with crossing of the direction ofthe fibers and with the interposition or a sheet of the above describedglue film between each of the layers of wood, and the whole is glued ina hot water press at 90 C. for 25 minutes under a pressure of 12-15kilos per square cm. A very well glued ply-wood sheet is thus obtained.When dried after remaining in cold water for 96 hours, or after boilingfor 3 hours in water, and its tensile strength tested, in all cases ahigh strength is obtained with a practically clean break.

Exanrra 14 252 parts of a crude melamine, which contains with 2 parts byvolume of water. The slightly turbid condensation solution is driedunder vacuum on plates, and a frothy, easily puverizable product isobtained. 200 parts or the dry product are dissolved in 200 parts byvolume or cold water and 2 parts of ammonium sulfate or 2 parts ofdibrom-cinnamic acid are added. An absorbent kraft paper having a weightof about grams per square metre is impregnated with this solution anddried in air. A non-hygroscopic glue fllm is thus obtained.

3 birch veneers of 1.4 mm. thickness are glued with this film at 80 C.under a pressure of 4 kilos per square cm. for minutes as described inExample 1. A very well glued ply-wood sheet is obtained having similargood properties to that obtained by Example 1.

What we claim is:

1. Water-proof binding agent comprising melamine-formaldehydecondensation product, starch and an ammonium salt capable of producingacid, in aqueous dispersion.

2. Binding agent comprising starch, melamineformaldehyde condensationproduct and an acid-' producing salt as an accelerator.

3. A binding agent comprising an aminotriazine-aldehyde condensationproduct, starch and an acid-producing salt as an accelerator.

GUSTAV WIDMER. WILLI FISCH.

